1. Field of the Invention
This invention relates to a high strength radial type ceramic turbine rotor, which is free from cracks in the proximity of a connection between a hub and a blade portion on an air exit side and a method of producing such a rotor.
2. Description of the Prior Art
Recently, silicon ceramic materials such as silicon nitride, silicon carbide, sialon and the like have been noticed utilized as structural materials for gas turbines, diesel engines and the like, because of their light weight and superior heat and thermal shock resistance. More particularly, radial type turbine rotors made of these ceramic materials have been highlighted for applications such as gas turbine rotors or turbo charger rotors for automobiles. Ceramic rotors are lighter and are capable of being used at much higher temperatures than metal rotors and are superior in thermal efficiency to the metal rotors. Moreover, as the radial type turbine rotors are complicated in shape, they are usually molded by injection molding or the like which forces the ceramic materials into narrow or curved portions or corners of the complicated shapes.
In order to form the rotors by injection molding the ceramic materials, it is necessary to add a great amount of plasticizer such as resin, wax or the like into the ceramic material. When the injection molded ceramic rotor body is heated or sintered to remove the resin or wax, the shape in the proximity of a connection between a hub and a blade portion on a gas exit side so rapidly changes that the resin or wax added as the plasticizer is not uniformly removed. Accordingly, the molded body is not uniform in density, so that locally different shrinkages occur in the body during sintering resulting in tensile forces which lead to cracks, particularly in the connection between the hub and blade portion on the gas exit side.